Lecture 11: How are cellular events controlled?

Question 1

What is the Nucleus?

Answer 1

• The most prominent organelle (5-10 µm)

- Contains most (but not all) of the cell’s genes

Question 2

How many nuclei can be found per cell?

Answer 2

• One in most cases
• RBC no nucleus
• Some muscle cells have multiple nuclei

Question 3

What is the function of the nucleus?

Answer 3

• It’s the repository (library) of genetic information

- Cell’s control centre (reciprocal relationship between cell and nucleus)

Question 4

What is the structure of the nucleus?

Answer 4

• Surrounded by the nuclear envelope / membrane

- Two phospholipid bilayer membranes (great for protection of DNA)

Question 5

What does the nuclear envelope look like?

Answer 5

• Looks like metal reinforcements (nuclear lamina)

- Composed of intermediate filaments

Question 6

What is the purpose of the nuclear envelope?

Answer 6

• Maintaining shape of nucleus

- Organising packaging of DNA

Question 7

What happens if nuclear lamina is defective?

Answer 7

• Hutchinson- Gilford Progeria Syndrome

Question 8

What is Hutchinson-Gilford Progeria Syndrome?

Answer 8

• It’s caused by defective nuclear lamina
• Nucleus folds in on itself and can’t handle DNA properly
• Accelerated ageing occurs
• Cells failing to regenerate themself

Question 9

What is the function of the nuclear pore?

Answer 9

• Controls what comes in and goes out of the nucleus
• mRNA, rRNA, tRNA
• Messenger, Ribosome, Transfer
• Allow control signals to move into the nucleus
• Energy and materials in

Question 10

What is the function of the nucleolus?

Answer 10

• Responsible for making the ribosomal rNA

Question 11

What is DNA?

Answer 11

• A nucleotide polymer

Question 12

Fun facts about DNA:

Answer 12

• Each human cell contains about 2.5m of DNA

- 250,00 x the diameter of the nucleus

Question 13

How does DNA fit into a nucleus?

Answer 13

• Very well packed ( must also be accessible)
• DNA double helix is combined with histone proteins to form chromatin fibres
• Chromatin fibres undergo multi-level packaging (Figure 16.22)

Question 14

How big is the DNA double helix? What is it’s function?

Answer 14

• 2nm diameter
• Helix interacts with specific histone (H2-H4) proteins (look like beads)
• To form 10nm diameter fibre
• Beads = nucleosome

Question 15

What further interaction occurs to package the DNA further?

Answer 15

• Histone (H1) + DNA
• Cause 10nm fibre to coil and form 30nm fibre
• 30nm fibre loops to form 300nm fibre

Question 16

What occurs during cell division?

Answer 16

• 300nm fibres coil to form metaphase chromosomes

Question 17

What is euchromatin?

Answer 17

• Less dense DNA
• Often genetically active (cell needs to use it at that time)
• Light

Question 18

What is heterochromatin?

Answer 18

• Dense DNA
• Genetically inactive (cell doesn’t need to use it at that time)
• Dark
• There is a dynamic relationship between euchromatin and heterochromatin

Question 19

Is the location of chromosome within the nucleus random?

Answer 19

• NO

- Is surprisingly organized